The invention relates to call control (CC) and in particular to the function of the so-called Call State Control Function (CSCF). The CSCF is typically included in a network node like a Call Processing Server (CPS).
The CSCF is the call control entity in the all-IP architecture responsible for supervising the call (or IP multimedia call). It handles the call establishment, supervision and disconnection signalling and may control resources associated with the call such as media gateways processing the various call related media streams.
The CSCF consists of two components: the Serving CSCF (S-CSCF) and the Interrogating CSCF (I-CSCF).
The Serving CSCF is used for mobile originated communications and also for supporting mobile terminated communications, it provides Serving Profile Database (SPD) and Address Handling (AH) functionality described below. The Serving CSCF supports the signalling interactions with the UE (User Entity). The Home Subscriber Server (HSS) is updated with the Serving CSCF address and the HSS sends the subscriber data to the Serving CSCF for storage.
The Interrogating CSCF is used for mobile terminated communications and is used to determine how to route mobile terminated calls. The Interrogating CSCF interrogates the HSS for information to enable the call to be directed to the Serving CSCF. The interrogating CSCF provides Incoming Call Gateway (ICGW) and AH functionality described below.
For mobile terminated communications both Serving CSCF and Interrogating CSCF functionality can be involved. For mobile originated communications Interrogating CSCF functionality is not required. Both Serving CSCF and Interrogating CSCF components can be provided in a single CSCF if required.
In the following, the CSCF functionality mentioned above is described in more detail.
The ICGW (Incoming call gateway) acts as a first entry point and performs routing of incoming calls. Furthermore, it performs an incoming call service triggering (e.g. call screening/call forwarding unconditional). Moreover, it performs a query address handling and communicates with the HSS.
The CCF (Call Control Function) carries out a call setup/termination and state/event management. It interact with MRF in order to support multi-party and other services, reports call events for billing, auditing, intercept or other purpose, and receives and processes application level registration. Furthermore, it also performs a query address handling. In addition, it may provide service trigger mechanisms (service capabilities features) towards Application & services network (VHE/OSA), may invoke location based services relevant to the serving network and may check whether the requested outgoing communication is allowed given the current subscription.
The SPD (Serving Profile Database) interacts with HSS in the home domain to receive profile information for the R00 all-IP network user and may store them depending on the SLA with the home domain. Furthermore, it notifies the home domain of initial user's access. In addition, it may cache access related information (e.g. terminal IP address(es) where the user may be reached etc.)
The AH (Address Handling) functionality performs analysis, translation, modification if required, address portability, and mapping of alias addresses. It furthermore may do temporary address handling for internetwork routing.
Moreover, an Originating CSCF (O-CSCF) is the CSCF where the originating party is registered and where the originating party services are handled (and the CCF functionality is invoked). On the other hand, the S-CSCF is the CSCF where the terminating party is registered and where the terminating party services are handled (using the CCF functionality).
During setup of a connection, a mobile station first transmits a setup message to the O-CSCF which, in turn, forwards a setup message to a CSCF acting as an I-CSCF. This CSCF, in turn, forwards a message to another CSCF which acts as an S-CSCF. The S-CSCF sends a setup message to the called party.
Thus, a setup for a connection is completed. However, during the setup procedure, it is difficult for a CSCF receiving a setup message to distinguish whether it should act as an I-CSCF or as an S-CSCF. For example, an I-CSCF does not have to perform the Call Control Function (CCF). Thus, it would be a waste of time and a waste of performance and capacity if a CSCF which is expected to act as an I-CSCF would act as an S-CSCF.
There are less optimal solutions for determining the mode the CSCF should operate in. For example, a less optimal method is shown in FIG. 9. According to FIG. 9, a SPD query is used for the decision. When an CSCF (in this example, the CSCF 93) receives a setup message form the O-CSCF 92, it performs an SPD query in order to find out whether the setup concerns a registered subscriber. Thus, it accesses its SPD 98. If the answer is yes, the CSCF identifies itself as an S-CSCF (as in the case of CSCF 95), otherwise (as it is in the case of CSCF 93), it identifies itself as an I-CSCF. If the CSCF identifies itself as an I-CSCF, the Location Request should then be done to the HSS 4. This problem does not only occur in the above-described examples. There are many situations in which a network element receiving a message like a setup message is not aware which function it should provide, i.e., in which mode it should operate.